(a) Field of the Invention
The present invention relates to a fabrication method of a semiconductor device, and more particularly to a method for fabricating a metal line of the semiconductor device, which is capable of reducing the height of a photoresist pattern and improving a photo margin.
(b) Description of the Related Art
A metal line to play an important role of power supply in a semiconductor device is a critical factor for determining a yield, operation speed and reliability of the device, and so, a technique for fabricating the metal line becomes increasingly important as a degree of integration of the device becomes high.
In general, the metal line of the semiconductor device is formed by forming a metal film by depositing aluminum or aluminum/copper alloy on a semiconductor substrate by means of a sputtering or evaporation method, and then patterning the metal film using a wet or dry etching method.
Recently, the dry etching method is being mainly used as the degree of integration of the semiconductor device becomes high.
The dry etching method uses plasma made by using special gases such as SiCl4, BCl3, Cl2, etc. Particularly, in forming the pattern of the metal line, the dry etching is performed by chemical reaction of chlorine radical (Cl) formed by the plasma with aluminum existing on a surface of a thin film for the metal line.
Now, a conventional general metal line fabrication method will be described as below.
First, an insulation layer is formed by depositing an oxide film on a semiconductor substrate on which devices or lower lines and the like are formed, and then an aluminum metal layer is formed on the insulation layer.
Subsequently, a photoresist pattern having openings of certain width is formed on the aluminum metal layer, a partial region of the aluminum metal layer is removed by dry etching using the photoresist pattern as a mask, and then the photoresist pattern is removed to form an aluminum metal line.
Examples of techniques for fabricating the metal line as described above are disclosed in U.S. Pat. Nos. 5,935,762, 6,006,764, 6,184,148, and 6,316,329.
However, for the fabrication of the metal line using the photoresist pattern, it is the biggest problem that the dry etching process has a bad selectivity with the photoresist.
Therefore, conventionally, the photoresist has to be formed at more than about 9,000 Å when a metal line having a critical dimension (CD) of less than 0.23 μm is to be formed.
However, a problem arises in that a random metal bridge phenomenon frequently occurs due to decrease of a photo margin as the photoresist pattern becomes thicker, and, to the contrary, when the photoresist pattern becomes thinner to increase the photo margin, a notching phenomenon occurs due to scarcity of the photo margin.